CN114502307B

CN114502307B - Tapping tool and method for machining threaded holes in workpieces

Info

Publication number: CN114502307B
Application number: CN202080057421.1A
Authority: CN
Inventors: P·科普顿
Original assignee: Audi AG
Current assignee: Audi AG
Priority date: 2019-09-04
Filing date: 2020-07-17
Publication date: 2024-01-30
Anticipated expiration: 2040-07-17
Also published as: DE102019123625A1; EP4025369A1; EP4025369B1; CN114502307A; DE102019123625B4; WO2021043488A1

Abstract

The invention relates to a tapping tool for machining a threaded bore (1) of a workpiece having an internal thread (9), wherein in a drilling path (B) the rotating tapping tool is tapped into the workpiece (5) until a target bore depth (t) is reached, while a bottom bore (51) is formed _B ) And guiding the tool out of the bottom hole (51) with a reverse feed amount and a rotational speed synchronized therewith in a reverse tapping stroke (G), wherein in a drilling stroke (B) the tapping tool is rotated in the same direction or in opposite directions relative to the reverse tapping stroke (G), wherein the tapping tool has a drill cutting portion (S1, S2) in which the bottom hole (51) is machined in the drilling stroke (B) and a thread machining portion (39) in which the internal thread (9) is machined in the reverse tapping stroke (G), wherein in the drilling stroke (B) the tool thread machining portion (39) remains unloaded and is not engaged with the bottom hole wall, and in the reverse tapping stroke (G) the tool drill cutting portion (S1, S2) remains unloaded and is not engaged with the machined internal thread (9).

Description

Tapping tool and method for machining threaded holes in workpieces

Technical Field

The invention relates to a tapping tool and a method for machining a threaded bore, in particular a threaded blind bore.

Background

In the so-called tapping process, both the bottom hole (i.e., the core hole) and the internal thread are drilled in a common tool path using a tapping tool. For this purpose, the tapping tool has at least one bottom hole cutter and a tool thread machining having at least one shaping tooth. In this method, a threaded hole drilling pass is first performed in which a rotating tapping tool is tapped into a workpiece without a bottom hole to a nominal hole depth. The reverse stroke is then followed, in which the tapping tool can be guided out of the threaded bore essentially without load.

In the prior art (for example, patent document WO 2019/029850 A1), internal threads are machined simultaneously with the drilling stroke. At the end of the drilling stroke, the direction of rotation of the rotating tool is reversed. The tool is then guided out of the threaded bore in a back-stroke without load.

Disclosure of Invention

The object of the present invention is to provide a tapping tool and a method for machining a threaded bore in a workpiece, in which the tool load is reduced compared to the prior art and the threaded bore can be machined in a shorter process time.

In contrast to the prior art described above, according to the invention, both the bottom hole and the internal thread are no longer machined at the same time during the drilling stroke. In contrast, in the present invention, the tapping tool is designed such that only bottom-hole drilling is performed during the drilling stroke. Subsequently, in the following reverse tapping pass, the internal thread is machined. Preferably, the drilling stroke and the counter tapping stroke are performed with a co-directional tool rotational movement. That is, a technically complex and time-consuming reversal of the direction of rotation in the changeover from the boring stroke to the counter-tapping stroke is dispensed with. The reverse tapping stroke is carried out with a reverse feed rate and a tool rotational speed synchronized therewith, whereby the tapping tool is guided out of the threaded bore with the formation of the internal thread.

The tapping tool is designed such that the tool thread machining (required for machining the internal thread) remains unloaded and does not engage the bottom hole wall during the drilling stroke. In the next reverse tapping pass, on the contrary, the tool drill cutting portion (required for machining the bottom hole) remains unloaded and does not engage the machined internal thread. During the back tapping stroke, the tool drill cutting portion moves radially inwardly of the radially inner thread crest of the internal thread with its drill cutting portion/edge. The reverse tapping stroke is performed on a tool axis that is parallel to the borehole axis.

At the end of the drilling stroke, a relief cut is made in order to prepare for the reverse tapping stroke. In the relief cutting, the rotating tapping tool is maneuvered radially by a radial offset and guided for circular rotational movement along a circular path about the bore axis.

The tapping tool has at least a first and a second drill cutting portion, the drill cutting portions being spaced apart from each other in the tool circumferential direction by a cutting edge angle. The cutting edge angle is designed such that the two drill cuts can be guided out of the workpiece threaded bore in a backtapping stroke without load and without engaging the machined internal thread.

In one embodiment, the thread-forming region formed on the tapping tool is arranged outside the rotation angle region formed by the two drill cutting regions in the tool circumferential direction.

As the tool rotates, the outer edge profiles of the two borehole cutters move on a circular trajectory of the borehole cutters. In the same way, the tooth profile of the tool thread machining moves on a circular track of the tooth profile having a tooth profile diameter as the tool rotates. In order to assist the relief cutting of a tapping tool without interference in the radial direction, the tooth profile diameter is designed to be smaller than the edge profile diameter. In this way, a radial tool free space is obtained between the circular trajectory of the borehole cutting part and the circular trajectory of the tooth profile. The tool free space is partially utilized in the radial direction during the relief cutting.

By way of example only, the edge angle formed between the first and second drill cutting portions is less than 180 ° and is, for example, in the range of 120 °.

In addition to the first and second drill cutting portions, the tapping tool may have at least one further third drill cutting portion, which may be positioned between the first and second drill cutting portions in the tool circumferential direction.

Each of the drill cuttings may have at least one transverse cutting edge configured at an end side on the tool tip. The transverse cutting edge of each drill cutting portion may transition into the longitudinal cutting edge of the drill cutting portion at a radially outer nose. In a specific embodiment, the drill cuts are each formed on a drill bridge extending in the longitudinal direction of the tool. The two hole drilling bridges can be spaced apart from one another in the tool circumferential direction by a chip receiving space. The cutting/rake/chip surfaces (in the tool circumferential direction) defining the chip volume can transition on the longitudinal cutting edge into the peripheral hole drilling bridge free surface. The guide ribs project radially outwards from each of the two free surfaces of the hole-drilling bridge. Furthermore, a tool thread can be formed on one of the two peripheral free faces of the hole-drilling bridge.

At the tool tip of the tapping tool, the cutting surface defining the chip-receiving space transitions on the end-side transverse cutting edge into the end-side free surface, which tapers conically in the direction of the tool axis. In terms of uniform drill cutting load, it is preferred that the first and second drill cutting parts are arranged in different height positions in the tool axial direction, that is to say are arranged with a height difference from each other in the axial direction. The axial height difference between the two drill cuttings, in particular the transverse edge of the drill cuttings with the associated nose, can be designed such that the drill cuttings loading of the individual drill cuttings is approximately the same during the drilling stroke. In the case of a height difference in the axial direction of the drill cutting part, an almost uniform drill cutting part loading can be achieved, in particular, although not the drill cutting part which is diametrically opposite with respect to the tool axis (as is the case, for example, in conventional tapping tools), so that the tooth feed of the individual drill cutting parts is almost equally large. In particular, the lateral cutting edges of the two end sides of the drill cutting portion may be level-different from each other in the tool axial direction.

In the process flow, the relief cut is performed after the drilling pass. In order to prepare the relief cutting, it is preferable to move the tapping tool, which is located deep in the desired hole, back by an axial offset counter to the drilling direction after the end of the drilling stroke. In this way, the tool tip is prevented from colliding with the bottom of the hole in the relief cutting.

In terms of defect-free thread machining, it is preferable for the tool rotation and the tool circumferential movement to take place in the same rotation and at the same rotational speed in the reverse tapping stroke.

Drawings

Embodiments of the present invention are described below with reference to the accompanying drawings.

Wherein:

FIG. 1 shows a threaded blind bore formed in a workpiece in a side cross-sectional view;

figures 2 and 3 show different views of the tapping tool;

fig. 4 to 8 show views illustrating the processing of the blind threaded hole shown in fig. 1 in a process flow;

FIGS. 9 and 10 show a conventional boring tool in different views;

fig. 11 to 14 show an embodiment of the present invention; and

fig. 15 to 18 show another embodiment of the present invention.

Detailed Description

In fig. 1, a finished threaded blind bore 1 is shown. The hole 1 is machined into the workpiece 5 by means of a so-called tap drilling process (which is explained later with reference to fig. 4 to 8) up to a nominal hole depth t _B With its hole bottom 3. The threaded bore 1 has a circumferential thread penetration 7 at its bore opening, which, in a further extension, transitions down into an internal thread 9. The internal thread 9 extends along the bore axis a to a usable theoretical thread depth t _G . As can also be seen from fig. 1, the thread of the internal thread 9 opens into an annularly encircling recess 13. In fig. 1, the thread inner crest of the internal thread 9 is located at the core diameter d _K And (3) upper part.

The blind threaded bore 1 shown in fig. 1 is machined by means of a tapping tool which is described next with reference to fig. 2 and 3. Thus, in fig. 2, the tool has a clamping shank 15, and the screw drill body 17 is coupled to the clamping shank 15. In fig. 3, a first and a second drill cutting portion S1, S2 are formed on the screw drill body 17, the drill cutting portions being spaced apart from each other in the tool circumferential direction u by a cutting edge angle α. In fig. 3, the tapping tool has two drill bridges 14 extending in the longitudinal direction of the tool. A drill cutting S1, S2 is formed on each of the two hole-drilling bridges 14. The two hole drilling bridges 14 are spaced apart from each other in the tool circumferential direction μ by a chip receiving space 23. Each of the drill cuts S1, S2 has a longitudinal cutting edge 27 (only shown in fig. 12 and 13) extending in the longitudinal direction of the tool and a transverse cutting edge 29 formed on the end face of the tool tip. The end-side transverse cutting edge 29 merges into the longitudinal cutting edge 27 at a radially outer nose 33.

The cutting/chip surfaces defining the chip space 23 transition on the longitudinal cutting edge 25 into the peripheral, hole-drilling bridge free surface 35 (fig. 3). Laterally projecting guide ribs 37 are each formed on the peripheral free surface 35 of the hole-drilling bridge. Furthermore, a tool thread 39 is formed on the wide hole-drilling bridge 14 (specifically on its hole-drilling bridge free surface 35). In fig. 3, the tool thread machining portion is composed of a total of three cutting teeth, i.e., a pre-cutting tooth 40, a middle tooth 41, and a finishing tooth 42. Alternatively or additionally, other teeth (e.g., teeth 43 shown in fig. 1) may also be provided. In fig. 3, the teeth 40 to 42 are arranged one behind the other in the tool circumferential direction u and are positioned at approximately the same height in the axial direction. However, the thread processing 39 is not limited to this particular embodiment variant. Conversely, fewer or more cutting teeth can also be provided and/or the cutting teeth can also be arranged axially offset from one another on the free surface 35 of the drill bridge.

As also seen in fig. 3, the outer edge profile of the first and second borehole cutting portions S1, S2 moves on a borehole cutting portion circular locus 45 having an edge profile diameter as the tool rotates. In the same manner, the tooth profile of the tool threaded bore machining 39 moves on a tooth profile circular trajectory or envelope curve 47 (fig. 3 and 4) having a tooth profile diameter as the tool rotates. In fig. 3 or 4, the tooth profile diameter is designed to be smaller than the edge profile diameter, whereby a tool free space 49 is obtained between the borehole cutting portion circular path 45 and the tooth profile circular path 47. The tool free space 49 is required in the relief cut F described later.

The working of a thread by means of a tapping tool according to the invention is described next with reference to fig. 4 to 8: thus, in the drilling stroke B (fig. 4 and 5), the rotating tapping tool is caused to tap into the workpiece 5 without the pilot hole in the case of forming the pilot hole 51, straightTo rated hole depth t _B . In the drilling stroke B, the two drilling cutters S1, S2 interact with the workpiece 5 in a cutting manner, while the tool thread machining 39 remains unloaded and is not engaged with the bottom hole wall. The tool axis W is oriented coaxially with the bore axis a, and the amount of feed and rotational speed of the tapping tool can be freely selected. The drilling process is preferably performed in a left-hand manner in the direction of rotation 38 shown in fig. 4.

Technically, a relief cut F follows immediately after the drilling stroke B (fig. 7). In order to prepare the relief cut F, after the end of the drilling stroke, the drill is brought to a nominal hole depth t _B The tapping tool is moved back by an axial offset deltaa (fig. 6) opposite the direction of drilling. It is thereby ensured that the tool tip is prevented from colliding with the hole bottom 3 during the relief cut F (fig. 7).

Next, a relief cut F (fig. 7) is made, in which the rotating tapping tool is steered radially by a radial offset Δr (fig. 7) and guided in a circular rotational movement along a circular trajectory 53 about the hole axis a. In the relief groove cutting F, an annular recess 13 is machined in the bottom hole wall without tool feed. A reverse tapping stroke G (fig. 8) is then carried out, in which, in a co-rotating movement (i.e. without reversal of the direction of rotation after the drilling stroke B), the tool is guided out of the workpiece threaded bore 1 with a reverse feed rate and a rotational speed synchronized therewith while the internal thread 9 is being formed. In the reverse tapping stroke G, the tool rotation and the tool circumferential movement are performed not only in the same rotational direction but also at the same rotational speed.

In general, in designing the drilling process step, the process parameters (that is to say the rotational speed n and the feed rate f of the drilling tool) and the position of the drill cuttings S1, S2 on the drilling tool are coordinated in such a way that the drill cuttings loading of the individual drill cuttings S1, S2 is approximately the same, that is to say ideally the feed rate v of the individual drill cuttings S1, S2 _fz (tooth feed) is the same. In conventional drilling tools (in fig. 9 and 10), this is achieved by a constant pitch between the drill cuttings S1, S2. Thus, in FIG. 9, the borehole is cutThe cutting portions S1, S2 are diametrically opposed with respect to the tool axis W, so that the feed amounts (tooth feed amounts) of the respective drill cutting portions S1, S2 are almost the same, as can be seen from fig. 10. In fig. 10, the circumferential surface of a conventional boring tool is shown in a constitutive manner. Accordingly, the drill cuttings S1, S2 are positioned at the same axial height H. In fig. 10, the drill cutting portions S1, S2 interact with the inner wall of the workpiece hole in a cutting manner by the same cutting width S, respectively. In fig. 10, the cutting travel w of two drill cuts S1, S2 obtained during drilling is shown ₁ And w ₂ . Cutting travel w ₁ And w ₂ Extending helically along the inner wall of the bore at a lead angle beta, whereby in the constitution diagram (fig. 10) a cutting stroke w is obtained ₁ And w ₂ Is a straight line of (c). In fig. 10, the cutting stroke w ₁ And w ₂ Instead, they do not overlap, but rather they transition into one another in the axial direction without overlapping.

In the embodiment of fig. 11 to 14, the pitch between the two borehole cuts S1, S2 is no longer the same (unlike the prior art according to fig. 9 and 10), but is different. Accordingly, in fig. 12, the feed amount f of each drilling cutting portion _fz The cutting portions are no longer identical for each borehole but are different. That is, in fig. 12, during the drilling process, the drill cutting portions S1, S2 are no longer subjected to uniformity, but are subjected to different loads. According to FIG. 12, the first borehole cutting section S1 is assigned the maximum feed v of the respective borehole cutting section _fz That is to say the first borehole cutting portion S1 is exposed to a greater cutting load. In fig. 12, the two drill cuttings S1, S2 are positioned at the same height H without an axial height difference Δh. According to fig. 13 and 14, each transverse cutting edge 29 of each drill cutting portion S1, S2 forms an acute angle β with the tool axis W ₁ 、β ₂ . In fig. 14, the acute angle β of the two drill cuts S1, S2 is equally designed (as in conventional drill tools with symmetrical drill cut distributions) ₁ 、β ₂ . Here, the acute angle beta is selected in such a way ₁ 、β ₂ So that on the circumference of the tool, i.e. at two boresThe difference in axial height Δh occurs at the tips 33 of the cutting portions S1, S2, specifically the different height positions H1, H2 of the drill cutting portions S1, S2, as shown in fig. 14.

In order to ensure an almost uniform loading of the drill cuttings S1, S2 despite the different pitches, in the embodiment of fig. 15 to 18 the drill cuttings S1, S2 are no longer positioned at the same axial height H, but are instead arranged at different height positions H1 and H2. The height positions H1 and H2 are chosen such that a more uniform drill cutting load of the two drill cutting portions S1, S2 is obtained compared to fig. 11 and 12. The height positions H1 and H2 are selected as a function of the process parameters during drilling (i.e. the tool rotational speed, the tool feed) and as a function of the respective pitch.

As can be seen from fig. 16, the drill cuts S1, S2 (similar to fig. 9 and 10) each interact with the inner wall of the hole in a cutting manner by means of the same cutting width S. In fig. 14, moreover, the cutting stroke w ₁ And w ₂ Not overlapping each other, but instead transitioning into each other without overlapping.

According to fig. 17 and 18, each transverse cutting edge 29 of each drill cutting portion S1, S2 forms an acute angle β with the tool axis W ₁ 、β ₂ . In fig. 18, the acute angle β of the two drill cutting portions S1, S2 ₁ 、β ₂ Instead of being designed identically (as in conventional drilling tools with symmetrical drilling cutting portion distribution), they are instead designed differently from one another. At this time, the acute angle beta is selected ₁ 、β ₂ The axial height difference Δh, or rather the different height positions H1, H2 of the drill cutting portions S1, S2, is present on the tool circumferential surface, i.e. on the tips 33 of the two drill cutting portions S1, S2, as is shown in fig. 16.

List of reference numerals

1 screw hole

3 hole bottom

5 work piece

7 thread countersink

8 chamfer angle

9 internal thread

13 retraction part

14-hole drilling bridging part

15 clamping handle

17 tool body

14. 16-hole drilling bridge

S1, S2 drilling and cutting part

23 chip containing space

25 longitudinal cutting edge

29 transverse cutting edge

30 free surface at end side

33 knife point

Free face of 35 hole drilling bridge

37 guide edge

38 in the direction of rotation in the drilling stroke

39 tool thread machining portion

40. Cutting teeth of 41, 42 screw thread processing parts

43 alternative cutting tooth

45 drilling cutting portion circular trajectory

Envelope curve of 47 thread machining 39

49 tool free space

51 bottom hole

53 circumference-circular track

t _B Rated hole depth

d _K Core diameter

u tool circumferential direction

Alpha blade angle

Axis of hole

W tool axis

B drilling travel

G reverse tapping stroke

F tool retracting groove cutting

Δr radial offset

Δa axial offset

ΔH height difference

Height position of H1 and H2

β ₁ 、β ₂ Acute angle

Claims

1. Tapping tool for machining a threaded bore (1) of a workpiece having an internal thread (9), wherein in a drilling path (B) the rotating tapping tool can be tapped into the workpiece (5) with the formation of a bottom hole (51) up to a nominal bore depth (t) _B ) In a reverse tapping stroke (G) in which the tapping tool can be guided out of the pilot hole (51) with a reverse feed rate and a rotational speed synchronized therewith, wherein in a drilling stroke (B) the tapping tool is rotated in the same direction or in opposite directions relative to the reverse tapping stroke (G), wherein the tapping tool has a drill cutting portion (S1, S2) in which the pilot hole (51) is machined in the drilling stroke (B) and a thread machining portion (39) in which the internal thread (9) is machined in the reverse tapping stroke (G), wherein in the drilling stroke (B) the tool thread machining portion (39) remains unloaded and is not engaged with the pilot hole wall, and in the reverse tapping stroke (G) the tool drill cutting portion (S1, S2) remains unloaded and is not engaged with the machined internal thread (9), wherein at the end of the drilling stroke, in order to prepare the reverse tapping stroke (G), a clearance cut (F) is performed, in which the tool is maneuvered to move radially around its tool axis of rotation (S) by at least one of the first and second tool axis of rotation (S1) and the tapping tool is guided radially around the drill cutting axis (S2) by at least one of the first and second rotational path (53), the drill cuts are spaced apart from each other in the tool circumferential direction (u) by a cutting edge angle (alpha), which is designed such that the two drill cuts (S1, S2) can be guided out of the workpiece threaded bore (1) in a non-load-bearing manner and without engaging the machined internal thread (9) during the reverse tapping stroke (G), and the tool thread machining (39) is arranged outside a rotation angle region (alpha) formed by the two drill cuts (S1, S2) in the tool circumferential direction (u).

2. Tapping tool according to claim 1, characterized in that the first and second drill cutting parts (S1, S2) move on a common drill cutting part circular trajectory (45) with a drill cutting part diameter when the tool is rotated, the tool thread machining part (39) moves in a drill stroke (B) on a diameter smaller than the bottom hole diameter with a radial tool free space (49) formed between the tool thread machining part (39) and the bottom hole wall, and the tool free space (49) is partly utilized in the radial direction when the tool is retracted for cutting (F).

3. Tapping tool according to any one of the preceding claims, characterized in that the tool thread machining (39) has at least one tapping tooth (40, 41, 42) and/or that each tapping tooth (40, 41, 42) is located on its own tooth profile diameter, wherein its difference indicates that the machining allowance between two successive tapping teeth and/or that the tapping tooth as the last tapping tooth (42) in the direction of rotation (38) is a finishing tooth with a tooth profile diameter that is greater than the tooth profile diameter of the preceding tapping tooth (41, 42) and/or that the tapping tooth (40, 41, 42) is located on the envelope curve (fig. 4; 4).

4. Tapping tool according to claim 3, characterized in that the at least one tapping tooth (40, 41, 42) is machined either in a cutting manner or in a forming manner or the at least one tapping tooth (40, 41, 42) is machined in a mixed manner not only in a cutting but also in a forming manner.

5. Tapping tool according to claim 1 or 2, characterized in that the first and second drill cutting portions (S1, S2) are arranged in different height positions (H1, H2) in the tool axis direction and have an axial height difference (Δh) with respect to each other.

6. Tapping tool according to claim 1 or 2, characterized in that the tool borehole cutting (S1, S2) has at least one third borehole cutting which is arranged in the tool circumferential direction (u) in a rotation angle region (α) between the first and second two borehole cutting (S1, S2).

7. Tapping tool according to claim 1 or 2, characterized in that each drill cutting portion (S1, S2) has at least one end-side transverse cutting edge (29) which is formed on the tool tip, the transverse cutting edges (29) of the two drill cutting portions (S1, S2) being offset from one another in height by a height difference (Δh) in the tool axial direction.

8. Tapping tool according to claim 7, characterized in that the transverse cutting edge (29) of each drill cutting portion (S1, S2) transitions at a radially outer nose (33) to a longitudinal cutting edge (fig. 14; 27), and/or that the drill cutting portions (S1, S2) are each formed on a drill bridge (14) extending in the longitudinal direction of the tool, and that the drill bridge (14) are spaced apart from each other in the circumferential direction (u) of the tool by chip receiving spaces (23), and/or that the cutting surfaces defining the chip receiving spaces (23) transition on the longitudinal cutting edge (27) to a peripheral drill bridge free surface (35), and/or that the guide ribs (37) each protrude from the peripheral drill bridge free surface (35), and/or that tool thread machining (39) is formed on the peripheral drill bridge free surface (35).

9. Tapping tool according to claim 8, characterized in that the transverse cutting edge (29) of each drill cutting portion (S1, S2) is at an acute angle (β) to the tool axis (W) ₁ 、β ₂ ) And the acute angle (beta) of the drilling cutting parts (S1, S2) ₁ 、β ₂ ) Acute angles (beta) of equal or drilling cutting portions (S1, S2) ₁ 、β ₂ ) Different from each other, whereby an axial height difference (Δh) occurs on the tool peripheral surface.

10. Tapping tool according to claim 9, characterized in that on the tool tip the cutting face defining the chip volume (23) transitions on the end-side transverse cutting edge (29) into an end-side free face (30) which tapers conically in the direction of the tool axis (W).

11. Tapping tool according to claim 1 or 2, characterized in that, in order to prepare the relief cut (F), the tapping tool is brought to a nominal hole depth (t _B ) Tapping tool and drilling hole at the sameThe direction is reversed by an axial offset (Deltaa) in order to avoid the tool tip colliding with the hole bottom (3) during the relief cutting (F).

12. Tapping tool according to claim 1 or 2, characterized in that in the reverse tapping stroke (G) the tool rotation and the tool circular movement are performed not only in the same rotational direction but also at the same rotational speed.

13. A tapping tool according to claim 3, characterized in that the tool thread machining portion (39) has a plurality of tapping teeth (40, 41, 42).

14. Tapping tool according to claim 5, characterized in that the axial height difference (Δh) between the two drill cutting portions (S1, S2) is designed such that the drill cutting portion load of the respective drill cutting portion (S1, S2) is almost identical in the drill stroke (B).